An important set of problems in perinatal biology concern the dynamics and control of placental respiratory gas exchange and fetal oxygenation. The proposed studies will test several hypotheses concerning the control of O2 consumption. For instance, we will test the hypothesis that fetal oxygen consumptioon is constant and unvarying. We will measure for the first time on a continuous basis the placental exchange rate and 02 consumption of the total uterine contents, the fetus, and the placenta plus uterus. We will explore the extent to which 02 consumption of these components are constant vs whether they change spontaneously in a dynamic manner. We will examine the extent to which uterine contractures, contractions, fetal breathing movements, and other factors affect O2 consumption. In addition, we will seek and understanding of whether O2 consumption of the fetus is affected by O2 content, O2 tension, or both. In addition, we will examine the dependency of fetal O2 consumption on increased temperature, resulting from maternal exercise. We will also determine the dose-response relations of fetal 02 consumption on increased temperature, resulting from maternal exercise. We will also determine the dose-response relations of fetal O2 consumption to the circulating concentrations of norepinephrine and triodothyronine infusion. We also will examine the role of both uterine and umbilical blood flows in affecting 02 consumption, the time constants of change, and the extent to which the blood flow on one side of the placental circulation alters to match that of the other. Taken as a whole these studies should markedly increase our understanding of the dynamics and control of placental 02 exchange, and fetal oxygen consumption.